Ask for the significance of 3ddot result

Dear AFNI experts,

I am trying to calculate spatial correlation between single subject PET and MRI with 3ddot, which i think is the proper command to use, right? the output seems to only contain one single r value, are there any way to get proper p value with such large DOF? I’ve seen spatial permutation test(spin test) in surface based analysis, but not appliable to my case, are there any similar solutions in AFNI?

Besides, what’s behind default 3ddot, since the result from 3ddot is not exactly the same as that calculate directly from afni_matlab

Best wishes,

[rp@localhost data]$ 3ddot MRI_26+tlrc. PET_26+tlrc

MRIOneDim = reshape(MRI,1,[]);
PETOneDim = reshape(PET,1,[]);
corrcoef(MRIOneDim, PETOneDim)
ans =
1.000000000000000 0.946982442535485
0.946982442535485 1.000000000000000

You may want to use the “-demean” option to remove the mean first.

That works, Great! Thanks, Dr.Glen.